The Demon Sword Master of Excalibur Academy, Vol. 4 (manga) — Yu Shimizu

At the evening party aboard the Hyperion, a group of terrorists take the fourth princess of the empire and the entire ship hostage. Time is running out for Leonis and his friends to rescue the princess and prevent everyone on the ship from sinking to their watery graves -- and what lurks beneath the surface is far more sinister than a mere rebellion. A dangerous mastermind sits at the center of the plot, and perhaps she holds a clue to the goddess Leonis has been seeking all this time…